1. Field of the Invention
The present invention relates to a heat exchanging element of laminated structure for use in a heat exchanging apparatus for conducting heat exchange between two fluids in the field of air conditioning. In particular, the invention relates to a total heat exchanging element for exchanging both latent heat and sensible heat.
2. Description of the Related Art
A total heat exchanging element of laminated structure typically used in the field of air conditioning heretofore comprises basic component members each of which is formed by laminating a partition member of flat shape and a spacing member of corrugated section. Here, the basic component members are laminated and bonded so as to make the directions of corrugation in their spacing members have substantially right angles with each other. The spacing members of this total heat exchanging element form flow paths. Airflows of different states (typically, airflows of different temperatures and humidities) are passed through the flow paths which adjoin in the direction of lamination so that latent heat and sensible-heat are exchanged between the both fluids across the partition members.
The partition members lie between the two airflows, existing as the medium for latent- and sensible-heat exchange. The heat conductivity and moisture permeability of the partition members thus have a large impact on the efficiency of the latent- and sensible-heat exchange of the total heat exchanging element. The spacing members have the role of maintaining the partition members at certain spacings to secure the flow paths for the two airflows to pass through.
In a total heat exchanging element intended for air conditioning, it is particularly necessary to reduce the transfer of such gases as carbon dioxide (CO2) between the two airflows. Both the partition members and the spacing members thus require a high gas barrier property aside from the foregoing capabilities.
Besides, the total heat exchanging element itself must have high flame retardancy in view of ensuring product safety. Various properties are thus required of the partition members and spacing members of the total heat exchanging element, and various types of partition members and spacing members have been used accordingly.
In one of conventional examples of the total heat exchanging element for exercising the foregoing capabilities, base paper is produced from slurry consisting chiefly of paper making fibers, mixed with a moisture absorbing/desorbing powder and a heat fusing substance. The base paper is impregnated with a flame retardant if necessary, and then provided with a moisture absorbing/desorbing coat on either or both sides to produce total heat exchanger paper. The resulting total heat exchanger paper is corrugated before laminated crosswise alternately (for example, see Japanese Patent Laid-Open Publication No. Hei 10-212691, pp. 3-4 and FIG. 1).
Another example is a total heat exchanger which is composed of flat liner sheets and corrugated sheets. The liner sheets are made of flame resisting paper formed by adding a flame retardant and a moisture absorbent to paper that consists chiefly of pulp. The corrugated sheets are made of a polypropylene film having no moisture absorbability. The corrugated sheets are joined with the liner-sheets interposed therebetween with their directions of corrugation orthogonal to each other alternately (for example, see Japanese Patent Laid-Open Publication No. 2001-241867, p. 2 and FIG. 1).
Still another example is a heat exchanger in which a plurality of flat partition plates are laminated with the intervention of corrugated spacer plates. Here, the corrugated spacer plates are made of base paper that is produced from a mixture of a ceramic fiber base material and a plant fiber base material, followed by impregnation of a flame retardant. The flat partition plates are also made of the same base paper impregnated with a flame retardant and a moisture absorbent (for example, see Japanese Patent Laid-Open Publication No. Sho 54-44255, pp. 1-2 and the drawings).
These conventional heat exchanging elements are characterized in that any of the partition members, i.e., the total heat exchanger paper, the liner sheets, and the partition plates contain a flame retardant and a moisture absorbent overlapping in lamination or in mixture.
Nevertheless, such conventional configurations with the overlapping flame retardant and moisture absorbent have the following problems.    1) Take the case of transferring latent heat, or equivalently, moisture between the two airflows flowing along the respective sides of each partition member. In the conventional configurations, not only a layer of moisture absorbent but also a layer of flame retardant lies in the direction of transfer of the moisture. Thus, even if the moisture is absorbed by the layer of moisture absorbent, the layer of flame retardant resists the moisture transfer so that the amount of the moisture transfer decreases in that part, with a drop in the moisture permeability of the partition member as a result.    2) Then, for the sake of still higher moisture permeability, it may be possible to increase the amount of the moisture absorbent. Nevertheless, the maximum total amount of chemicals capable of application or impregnation to a unit area of the base material of the partition member is limited. In the conventional configurations where the moisture absorbent and the flame retardant are both applied to the same portion of the partition member, an increase in the amount of the moisture absorbent thus decreases the amount of the flame retardant with a drop in flame retardancy. The same holds vice versa, adding up to another problem of a trade-off between the moisture absorbability and the flame retardancy.    3) Furthermore, since the moisture absorbent and the flame retardant are used in the same portion, deliberate selections of the two chemicals are required so as not to react with each other easily because of their contact. This means another problem which is a narrow choice of the moisture absorbent and the flame retardant. The narrow choice should be avoided as far as possible since it causes higher product cost.
As described in Japanese Patent Laid-Open Publication No. Sho 54-44255, moisture absorbability and flame retardancy may be provided simultaneously by impregnating the partition members with a flame retardant having moisture absorbability. This moisture absorbability, however, is not as high as that of a moisture absorbent, and it is therefore difficult to achieve exchange efficiency higher than with a moisture absorbent alone. In addition, the same problem as the foregoing problem 3) also occurs in that such a flame retardant has only a limited choice.